Interference detection in a frequency modulated continuous wave (fmcw) radar system

ABSTRACT

A frequency modulated continuous wave (FMCW) radar system is provided that includes a receiver configured to generate a digital intermediate frequency (IF) signal, and an interference monitoring component coupled to the receiver to receive the digital IF signal, in which the interference monitoring component is configured to monitor at least one sub-band in the digital IF signal for interference, in which the at least one sub-band does not include a radar signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/120,129, filed Aug. 31, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/679,461, filed Apr. 6, 2015 (now U.S. Pat. No.10,067,221), all of which are hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

Embodiments of the present disclosure generally relate to radar systems,and more specifically relate to detection of interference in a frequencymodulated continuous wave (FMCW) radar system.

Description of the Related Art

Multiple radars operating simultaneously in a limited region have thepotential to interfere with each other. This simultaneous operation cancause degradation in signal-to-noise ratio, potentially masking smallobjects, as well as cause ghost objects to appear. For frequencymodulated continuous wave (FMCW) radar systems, this interferencetypically manifests itself over a short window of time within a chirp,and it is desirable to know when the interference occurs so thatmitigation and/or avoidance techniques can be applied.

Current radar systems identify interference by measuring the variationof the power in the signal band during a chirp. While such systemsmeasure the interference directly as it is happening, the measurementsare corrupted by the presence of reflected signals also present in thesignal band due to the desired operation of the radar.

SUMMARY

Embodiments of the present disclosure relate to methods and apparatusfor interference detection in a frequency modulated continuous wave(FMCW) radar system. In one aspect, a frequency modulated continuouswave (FMCW) radar system is provided that includes a receiver configuredto generate a digital intermediate frequency (IF) signal, and aninterference monitoring component coupled to the receiver to receive thedigital IF signal, in which the interference monitoring component isconfigured to monitor at least one sub-band in the digital IF signal forinterference, in which the at least one sub-band does not include aradar signal.

In one aspect, a method for interference detection in a frequencymodulated continuous wave (FMCW) is provided that includes receiving, inan interference monitoring component of the FMCW radar, a digitalintermediate frequency (IF) signal from a receiver in the FMCW radar,and monitoring, by the interference monitoring component, at least onesub-band in the digital IF signal for interference, in which the atleast one sub-band does not include a radar signal.

In one aspect, a frequency modulated continuous wave (FMCW) radar systemis provided that includes a receiver configured to generate a digitalintermediate frequency (IF) signal during transmission of a frame ofchirps, a digital front end (DFE) component coupled to the receiver toreceive the digital IF signal, in which DFE is configured to extract aradar signal band from the digital IF signal, and an interferencemonitoring component coupled to the receiver to receive the digital IFsignal, in which the interference monitoring component is configured tomonitor each sub-band of a plurality of sub-bands in the digital IFsignal for interference, in which the radar signal band is not includedin the plurality of sub-bands.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments will now be described, by way of example only,and with reference to the accompanying drawings:

FIG. 1 and FIG. 2 are examples;

FIG. 3 and FIG. 4 are block diagrams of an example frequency modulatedcontinuous wave (FMCW) radar system;

FIG. 5 is a block diagram of the digital front end (DFE) component ofFIG. 4;

FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are examples illustrating methods forinterference detection in the FMCW radar system of FIGS. 3-5; and

FIG. 10 is a flow diagram of a method for interference detection in theFMCW radar system of FIGS. 3-5.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

Specific embodiments of the disclosure will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency.

As previously mentioned, degradation in signal-to-noise (SNR) in anautomotive radar system such as a FMCW radar system may occur due tointerference introduced by multiple radar systems operatingsimultaneously. The degradation in SNR may potentially mask smallobjects and/or cause detection of ghost objects. If the interference canbe detected when it occurs, steps may be taken to mitigate and/or avoidthe interference.

As shown in the example of FIG. 1, in a frequency modulated continuouswave (FMCW) radar system, a ramp waveform, also referred to as asaw-tooth waveform, is used to generate a signal with linearly varyingfrequency in the time domain. The variation of the instantaneousfrequency is proportional to the ramp waveform. The generated signal istransmitted and the delayed signal, as reflected from any objects inview of the radar, is received. The velocity and distance of the objectscan be estimated from the intermediate frequency (IF) band in thereceived signal. Distance is measured by the frequency differenceestimating the round-trip delay. Velocity is estimated by observing thesame object across multiple chirps and looking at the phase rotation ormovement of the frequency difference.

The example of FIG. 2 illustrates an interference signal crossing thereceived signal over time. Interference from other sources disturbs theFMCW radar only when the frequency offset of an interfering signal iswithin the IF bandwidth of the receiver. A crossing interference signalappears “impulse-like” in the baseband of the radar, which leads to anelevation of the noise floor in post-reception measurements. Currenttime and frequency domain interference mitigation solutions rely onknowing when the interference occurs. Current techniques for detectingwhen the interference occurs examine the in-band energy which means thatthe interference can be detected only if the interference issignificantly higher than the many present desired reflected signalsfrom the scene. In other words, in such techniques, the threshold fordetection of unwanted interference is above the threshold at which lossof scene dynamic range occurs. The interference must be similar to orlarger than the largest reflected signal and is much larger than faintreflections, which are already lost.

Embodiments of the disclosure provide for detection of interferencebased on energy in one or more sub-bands of the IF signal that do notinclude desired radar reflections. More specifically, embodimentsdetermine whether or not interference is present in the sub-band wheredesired radar reflections are expected, i.e., the desired signal band orradar signal band, by examining the energy over time in at least onesub-band of the IF signal where reflected signals are not expected to bepresent. Interference is detected in a quiet region of the IF signaluncorrupted by desired radar reflections. Therefore, a higher SNR thanprior art techniques operating on the radar signal band is achieved andsmaller levels of interference can be detected. Further, in someembodiments, the time during a chirp when the interference is presentcan be localized.

FIG. 3 is a block diagram of an example FMCW radar system 300 configuredto perform interference detection during operation of the radar system300. The example FMCW radar system 300 includes a radar system-on-a-chip(SOC) 302, a processing unit 306, and a network interface 308. Thearchitecture of the radar SOC 302 is described in reference to FIGS. 4and 5.

The radar SOC 302 is coupled to the processing unit 306 via a high speedserial interface. As is explained in more detail in reference to FIG. 4,the radar SOC 302 includes functionality to generate multiple digitalintermediate frequency (IF) signals (alternatively referred to asdechirped signals, beat signals, or raw radar signals) that are providedto the processing unit 306 via the high speed serial interface. Further,as described in more detail in reference to FIG. 5, the radar SOC 302includes functionality to perform interference monitoring in IF signalsin which received signal strength indicator (RSSI) numbers are generatedover time. As is well known, RSSI is an indication of the power level ofthe signal being received by a receive antenna. Therefore, the higherthe RSSI number, the stronger the signal. Quantized RSSI numbers areprovided to the processing unit 306 to be used for interferencefrequency detection and interference mitigation.

The processing unit 306 includes functionality to perform radar signalprocessing, i.e., to process the received radar signals to determine,for example, distance, velocity, and angle of any detected objects. Theprocessing unit 306 may also include functionality to perform postprocessing of the information about the detected objects, such astracking objects, determining rate and direction of movement, etc.Further, the processing unit 306 includes functionality to performinterference frequency detection based on the quantized RSSI numbers andto perform interference mitigation. Interference frequency detection andoptions for interference mitigation are described in more detail herein.

The processing unit 306 may include any suitable processor orcombination of processors as needed for the processing throughput of theapplication using the radar data. For example, the processing unit 306may include a digital signal processor (DSP), a microcontroller (MCU),an SOC combining both DSP and MCU processing, or a field programmablegate array (FPGA) and a DSP.

The processing unit 306 provides control information as needed to one ormore electronic control units in the vehicle via the network interface308. Electronic control unit (ECU) is a generic term for any embeddedsystem in a vehicle that controls one or more the electrical system orsubsystems in the vehicle. Types of ECU include, for example,electronic/engine control module (ECM), powertrain control module (PCM),transmission control module (TCM), brake control module (BCM or EBCM),central control module (CCM), central timing module (CTM), generalelectronic module (GEM), body control module (BCM), and suspensioncontrol module (SCM).

The network interface 308 may implement any suitable protocol, such as,for example, the controller area network (CAN) protocol, the FlexRayprotocol, or Ethernet protocol.

FIG. 4 is a block diagram of the radar SOC 302. The radar SOC 302 mayinclude multiple transmit channels 404 for transmitting FMCW signals andmultiple receive channels 402 for receiving the reflected transmittedsignals. Further, the number of receive channels may be larger than thenumber of transmit channels. For example, an embodiment of the radar SOC302 may have two transmit channels and four receive channels.

A transmit channel includes a suitable transmitter and antenna. Areceive channel includes a suitable receiver and antenna. Further, eachof the receive channels 402 are identical and include a low-noiseamplifier 406,408 to amplify the received signal, a mixer 410, 412 tomix the transmitted signal with the received signal to generate an IFsignal, a baseband bandpass filter 414, 416 for filtering the IF signal,a variable gain amplifier (VGA) 415, 417 for amplifying the filtered IFsignal, and an analog-to-digital converter (ADC) 418, 420 for convertingthe analog IF signal to a digital IF signal. The bandpass filter, VGA,and ADC of a receive channel may be collectively referred to as abaseband chain or baseband filter chain. The mixers 406, 408 generateboth the in-phase (I) and quadature (Q) components of the IF signal. TheI component may be generated by mixing the incoming signal withcos(w_(LO)*t) and the Q component may be generated by mixing theincoming signal with sin(w_(LO)*t) where t is time in seconds andw_(LO)=2*π*f_(LO) (units are radians/s) where f_(LO)(t) is theinstantaneous frequency of the transmitter at time t.

The receive channels 402 are coupled to a digital front end (DFE)component 422. The DFE 422 includes functionality to perform decimationfiltering on the digital IF signals to reduce the data transfer rate.The DFE 422 may also perform other operations on the digital IF signals,e.g., DC offset removal. The DFE 422 further includes functionality toperform interference monitoring on the digital IF signal from one of thereceive channels 402. This functionality is described in reference toFIG. 5. The DFE 422 is coupled to a high speed serial interface (I/F)424 to transfer the decimated digital IF signals and the output of theinterference monitoring to the processing unit 106.

The serial peripheral interface (SPI) 426 provides an interface forcommunication with the processing unit 306. For example, the processingunit 306 may use the SPI 426 to send control information, e.g., timingand frequencies of chirps, output power level, triggering of monitoringfunctions, etc., to the control module 428. The radar SOC 302 may usethe SPI 426, for example, to send the results of monitoring functions tothe processing unit 306.

The control module 428 includes functionality to control the operationof the radar SOC 302. In particular, the control module 428 includesfunctionality to receive chirp control information from the processingunit 306 and to use this control information to generate chirpparameters for the timing engine 432. The control module 426 mayinclude, for example, an MCU that executes firmware to control theoperation of the radar SOC 302 and to perform various monitoringfunctions.

The programmable timing engine 432 includes functionality to receivechirp parameter values for a sequence of chirps in a radar frame fromthe control module 428 and to generate chirp control signals thatcontrol the transmission and reception of the chirps in a frame based onthe parameter values. The chirp parameters are defined by the radarsystem architecture and may include, for example, a transmitter enableparameter for indicating which transmitters to enable, a chirp frequencystart value, a chirp frequency slope, an analog-to-digital (ADC)sampling time, a ramp end time, a transmitter start time, etc.

The radio frequency synthesizer (SYNTH) 430 includes functionality togenerate FMCW signals for transmission based on chirp control signalsfrom the timing engine 432. In some embodiments, the RSYNTH 430 includesa phase locked loop (PLL) with a voltage controlled oscillator (VCO).

The clock multiplier 440 increases the frequency of the transmissionsignal (LO signal) to the LO frequency of the mixers 406, 408. Theclean-up PLL (phase locked loop) 434 operates to increase the frequencyof the signal of an external low frequency reference clock (not shown)to the frequency of the SYNTH 430 and to filter the reference clockphase noise out of the clock signal.

FIG. 5 is a block diagram of the DFE 422 illustrating both theinterference monitoring functionality and the normal processing of IFsignals. As previously mentioned, the digital IF signal from one of thereceive channels 402 is monitored for interference. The block diagram isexplained assuming that the digital IF signal from the ADC 418 is theone being monitored. Further, the ADC 418 is assumed to be a complexoversampling ADC. If the receive antennas are symmetric, then allreceive channels have a similar view of any interference and any of thereceive channels may be monitored for interference. If the receiveantennas are not similar, then a receive channel with the widestbeamwidth may be selected for monitoring in order to better detect anyinterfering signals.

The decimate component 502 of the DFE 422 receives the digital IF signalfrom the ADC 418 and decimates the signal for further processing. Thedecimated IF signal is then passed to both the normal processing path ofthe DFE 422 and the interference monitoring component 512. The normalprocessing path extracts the radar signal band from the decimated IFsignal and further reduces the sample rate before the radar signal isoutput to the processing component 306. The desired radar signal bandoccupies from [0, f_(IFBW)] in the IF signal. The first decimationcomponent 504 includes the desired signal of bandwidth [0, f_(IFBW)]with a minimum output sample rate of 2*f_(IFBW). For real decimationfilters, this signal also includes all of the information in [−f_(IFBW),0] which may contain unwanted interference. The frequency shiftercomponent 506 moves the desired band to [−f_(IFBW)/2, f_(IFBW)/2] andthe undesired band to |f|>f_(IFBW)/2. The final decimation component 508reduces the output sample rate to f_(IFBW) without any loss of desiredband information.

The amount of decimation depends on the ratio of oversampling in the ADC418 and the sub-bands monitored by the interference monitoring 512. Fora sigma delta ADC, the oversampling ratio (OSR) (and hence totaldecimation ratio) is typically between 16 and 128, depending on desiredSNR, order of the modulator, speed of the transistors, etc. For apipeline or SAR (successive approximation register) ADC, theoversampling decimation ratio is typically 1-4 depending on therequirements of the analog anti-aliasing filter. In some embodiments,the ADC 418 is a sigma delta ADC. The total decimation ratio of thedecimation components 502 and 504 equals the OSR. The decimationperformed by the decimation component 502 is smaller than that of thedecimation component 504 such that the out-of-band region is notcompletely removed. The out-of-band region is cleaned up by thedecimation component 504 for the normal processing path. The output ofthe decimation component 502, which contains the out-of-bandinformation, is used for interference monitoring. If the second Nyquistband is used for interference detection, the decimation component 502 isreduced by half and the decimation component 504 performs the final 2×decimation. If additional bands are used for interference detection, thedecimation of the decimate component 502 and the decimate component arereduced accordingly.

The interference monitoring component 512 may include one or moreinterference monitoring paths 513. As will be better understood from theinterference detection method descriptions of FIGS. 6-9, in variousembodiments, one or more sub-bands of the IF signal may be monitored forinterference. A sub-band may be a part of the band of the IF signal ormay be the full band. If a maximum of N sub-bands can be concurrentlymonitored in a particular embodiment, then the DFE 422 includes Ninterference monitoring paths 513. The number of sub-bands that can beconcurrently monitored in a particular radar system is a designdecision.

An interference monitoring path 513 monitors a particular sub-band forinterference, generating RSSI numbers over time and outputting quantizedRSSI numbers indicative of one or more levels of interference in themonitored sub-band. The frequency shifter component 514 and the low passfilter component 516 operate to extract a sub-band of frequencies[f_(iL), f_(iU)], where i=1, . . . , N and f_(L) and f_(U) are the lowerand upper ends of the sub-band. The frequency shifter component 514shifts the IF signal by −(f_(iU)+f_(iL))/2 such that the relevant bandis centered at [−f_(BW), +f_(BW)] where 2f_(BW)=|f_(iL)−f_(iU)|. The lowpass filter component 516 outputs a signal of bandwidth f_(BW).

The instantaneous power finder component 518 determines theinstantaneous power of the sub-band signal. As is well known,instantaneous power is the power in a signal at the time the measurementis made. The instantaneous power finder component 518 determines theinstantaneous power as I²+Q². The instantaneous power is calculated forevery sample m at the output of the low pass filter component 516. Eachsample m corresponds to a different time point t=m*T_(s), where T_(s) isthe sampling rate of the system.

The moving average filter component 520 determines the RSSI number ofthe sub-band signal at time t. As is well known, a moving average filteraverages values across a fixed subset of sequential incoming values, inwhich as a new sample comes in, the oldest sample is dropped from thesubset and the new sample is added. The size of the fixed subset, whichis also referred to as the width of the moving average filter, may beprogrammable and may be selected based on the relative rate at whichinterference is expected to cross the IF signal. A wider moving averagefilter will reduce noise but may tend to suppress rapidly movinginterference signals. In some embodiments, the width may be varied,e.g., 0.5 to 10 us, based on the ramp rate where faster ramp rates willresult in narrower filter widths.

In some embodiments, the output of the moving average filter component520 is an RSSI value for each incoming sample. In some embodiments, theoutput of the moving average filter is decimated such that the output ofthe moving averaging filter component 520 is at a lower sample rate. Theamount of decimation may be programmable and the decimation ratioselected as a tradeoff between more precisely localizing anyinterference (smaller decimation ratio preferred) and the amount of datasent to the processing unit 306 (higher decimation ratio preferred).

The interference threshold component 522 quantizes the RSSI numbers fromthe moving average filter component 520 using three interferencethresholds, E1, E2, and E3. The thresholding performed by theinterference threshold component 522 is a quantization process thatconverts an RSSI number, which may be, for example, sixteen bits, into atwo bit number, i.e., an interference impact indicator, that containssufficient information to allow the processing unit 306 to makedecisions regarding any detected interference. This quantizationsignificantly reduces the data rate to the processing unit 306 withoutlosing the information needed to detect medium and large amplitudeinterference. Table 1 illustrates the use of the three thresholds. Theparticular values of the thresholds and the two bit encoding for theimpact indicators are implementation dependent and may be programmablein some embodiments.

TABLE 1 RSSI Number Impact <E1 No interference El−E2 Moderateinterference → slight radar degradation E2−E3 High interference → mediumradar degradation >E3 Severe interference → no radar operation possible

The output of the interference monitoring component 512 may becharacterized as

[n], i.e., the quantized RSSI (interference impact indicator) of the kthfrequency sub-band at the nth time step. In one embodiment, the

[n] values for each of the monitored sub-bands are interleaved whentransmitted to the processing unit 306, e.g.,

[0n],

[0], . . . ,

[0],

[1], . . . , where M is the number of monitored sub-bands. Theprocessing unit 306 then sorts the interleaved values into individualstreams for each sub-band. In another embodiment, the values are passedto the processing unit 306 as a triplet (k, n,

[n]), which is useful if not all of the values are passed to theprocessing unit 306, e.g., not sending any information for RSSI<E1.

The processing unit 306 can use the impact indicators for a sub-band kto determine information such as the frequency of any interference andthe time of the interference. For example, assume that interference ispresent between

[n1, n2], where the sampling rate of the impact indicators is 1 μs.Thus, the detected interference is present for (n2−n1)*1 μs. If sub-bandk covers IF frequencies [f_(A), f_(B)], then the relative frequencyslope magnitude of the interference versus the LO of the radar is

${\frac{f_{A} - f_{B}}{\left( {{n2} - {n1}} \right)*1\mspace{14mu}{µs}}}.$

Further, the sign of the relative slope can be determined by looking atan adjacent sub-band if multiple sub-bands are being monitored. Ifsub-band k+1 covers IF frequencies [f_(B), f_(C)] and the interferenceis present in sub-band k+1 after sub-band k, the sign the relative slopecan be determined as sign(f_(C)−f_(A)).

FIG. 6 is an example illustrating a method for interference detectionthat can be performed in the radar system 300. In this method, theinterference monitoring is performed during chirp transmissions, i.e.,the transmitters are on. Interference monitoring is performed in one ormore of the sub-bands of the IF signal outside the band having theexpected reflected signal, i.e., the radar signal band. For example, twosub-bands may be monitored as depicted in FIG. 7, i.e., the image band(or a sub-band thereof) and the 2^(nd) (upper) Nyquist band (or asub-band thereof). With this method, interference crossing the radarsignal band or “close-by frequency” interference which may potentiallymove into the radar signal band can be detected.

More specifically, during a chirp, the reflected signal is expected inthe frequency range

${f_{c}(t)} + {\frac{B}{T_{r}}*\left( {0,{MaxRoundTripDelay}} \right)}$

where f_(c)(t) is the current transmitted frequency, B is the bandwidthof the IF signal and T_(r) is the length of the chirp ramp. The value ofMaxRoundTripDelay depends on the target range of the radar system 300.If the target range is Dmax meters, then MaxRoundTripDelay=2*Dmax/c,where c is the speed of light. This corresponds to a radar signalintermediate frequency range of (0,F_(Beatmax))Hz where F_(BeatMax) isB/Tr*(2Dmax/c). Thus, the frequency range of the image band is(−F_(Beatmax), 0) and the frequency range of the upper Nyquist band is(F_(BeatMax)+Δ₁, F_(BeatMax)+Δ₂) where the values of Δ₁ and Δ₂ may bechosen based on ease of implementation.

The intent of this method is to measure interference in a sub-bandwithout other energy present in the sub-band. The limitations on thismethod may be: (1) in the image band, there may be energy that foldedover from the radar signal band; and (2) in the second Nyquist band,there may be weak reflections from distant objects, harmonic distortionand intermodulation from objects in the radar signal band, and excessquantization noise from the oversampling ADC. However, the ratio ofinterference to non-interference may be increased by 40 dB by measuringinterference outside of the radar signal band.

To implement this method for two sub-bands, the interference monitoringcomponent 512 includes at least two interference monitoring paths 513.In one of the monitoring paths, the frequency shifter component 514 andthe low pass filter component 516 are configured to extract the imagesub-band and in another of the monitoring paths, the frequency shiftercomponent 514 and the low pass filter component 516 are configured toextract the upper Nyquist sub-band. The interference monitoringcomponent 512 generates interference impact indicators for each of thesesub-bands.

The processing unit 306 may use the received interference impactindicators for the two sub-bands to mitigate the presence ofinterference. For example, if the interference impact indicatorsindicate the presence of severe or high interference in one or both ofthe sub-bands, the processing unit 306 may mark the corresponding timesamples within corresponding chirps that occur near the detectedinterference as corrupted. In particular, given that the two sub-bandsstraddle the radar signal band, if interference is detected first in onesub-band and then, after a gap, in the other, the chirp samples inbetween are likely corrupted by interference and can be marked.

The radar signal processing in the processing unit 306 can then use thisinformation to mitigate the impact of the corrupted chirps. In anotherexample, the processing unit 306 may zero out all samples for theprevious chirps from all receive channels 402 and/or the next chirps. Inanother example, the processing unit 306 may use this information tochange the frequency for subsequent chirps in the frame and/or for asubsequent frame of chirps.

FIG. 7 is an example illustrating a method for interference detectionthat can be performed in the radar system 300. In this method, theinterference monitoring is performed between chirp transmissions in aframe of chirps. After each chirp during the chirp recover/blank time,the transmitters are turned off and a scan in the active frequency rangeof the chirp is performed. In a 77 GHz radar system, this activefrequency range can be anywhere from 100 Mhz to 4 GHz depending on thechirp configuration. During the scan, the LO frequency is varied as aresult of the ramp back of the LO and interference impact indicators aregenerated by the interference monitoring component 512 from the signalreceived in the monitored receive channel 402. In this method, onesub-band of the IF signal is monitored which is the full bandwidth ofthe IF signal.

The processing unit 306 may use the received interference impactindicators to mitigate the presence of interference. For example, theprocessing unit 306 may use the received indicators to create afrequency occupancy map of which frequencies have interference and thestrength of the interference. The map can be of a single scan or anaccumulation of scans. After observing the strength and frequency of theinterference, the processing unit 306 can select a suitable band forfuture transmission with a minimum interference over a contiguousfrequency spectrum.

Note that the methods of FIGS. 6 and 7 can be used simultaneously.During the “up” ramp of a chirp, the method of FIG. 6 can be performedin which interference can be measured in neighboring sub-bands of theradar signal band, and corrupted samples in corresponding chirps can bedetected. During the “down” ramp when the transmitters are off, themethod of FIG. 7 can be performed to track the bands where interferenceis present.

FIG. 8 is an example illustrating a method for interference detectionthat can be performed in the radar system 300. In this method, theinterference monitoring is performed before the transmission of a frameof chirps while the transmitters are off. In this method, a scan of thefull frequency range, e.g., 4 GHz, is performed. During the scan, the LOfrequency is varied and interference impact indicators are generated bythe interference monitoring component 512 from the signal received inthe monitored receive channel 402. In this method, one sub-band of theIF signal is monitored which is the full bandwidth of the radar system300.

The processing unit 306 may use the received interference impactindicators to mitigate the presence of interference. For example, theprocessing unit 306 may use the indicators to determine interferencefree frequencies. The processing unit 306 may then program the radar SOCto use an identified interference free frequency range for transmissionof the subsequent frame of chirps.

FIG. 9 is an example illustrating a method for interference detectionthat can be performed in the radar system 300. In this method, theinterference monitoring is performed during the chirp recover/blank timebetween selected chirp transmissions in a frame of chirps. That is, theinterference monitoring may be performed, for example, after each chirp,between subsets of chirps, or after chirps with a sufficient bandwidthdown ramp. In this method, a scan of the full frequency range, e.g., 4GHz, is performed. During the scan, the LO frequency is varied andinterference impact indicators are generated by the interferencemonitoring component 512 from the signal received in the monitoredreceive channel 402. In this method, one sub-band of the IF signal ismonitored which is the full bandwidth of the radar system 300.

The processing unit 306 may use the received interference impactindicators to mitigate the presence of interference. For example, theprocessing unit 306 may use the indicators to determine interferencefree frequencies. The processing unit 306 may then program the radar SOCto use an identified interference free frequency range for transmissionof subsequent chirps in the frame and/or for transmission of the nextframe of chirps.

FIG. 10 is a flow diagram of a method for interference detection thatcan be performed in the radar system 300. This method may be performedcontinuously while the radar system 300 is operating. Initially, adigital IF signal is received 1000 from the receiver (receive channel)in the radar system 300 that is being monitored to detect interference.The digital IF signal is received in the interference monitoringcomponent 512. The interference monitoring component 512 monitors 1002one or more sub-bands (depending on the method embodiment) in thedigital IF signal for interference. In some embodiments, one sub-band ismonitored. Examples of such monitoring are previously described herein.In some embodiments, multiple sub-bands are monitored. Examples of suchmonitoring are previously described herein.

Other Embodiments

While the disclosure has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the disclosure as disclosed herein.

For example, embodiments have been described herein in which theinterference frequency detection and interference mitigation processingis performed by a processing unit in the radar system external to theradar SOC. One of ordinary skill in the art will understand embodimentsin which some or all of such processing is performed by a processingunit on the SOC, e.g., the control module of the SOC or anotherprocessor on the SOC.

In another example, embodiments have been described herein in which aclock multiplier is used. One of ordinary skill in the art willunderstand embodiments in which the multiplier is not needed because theSYNTH operates at the LO frequency rather than a lower frequency.

In another example, embodiments have been described herein in which thetransmission signal generation circuitry is assumed to a radio frequencysynthesizer. One of ordinary skill in the art will understandembodiments in which this circuitry is an open loop oscillator (radiofrequency oscillator) plus a digital-to-analog converter (DAC) or othersuitable transmission signal generation circuitry.

In another example, embodiments have been described herein in whichinterference monitoring is performed on a single receive channel whenmultiple receive channels are present. One of ordinary skill in the artwill understand embodiments in which more than one receive channel ismonitored for interference. For example, if receiver antennas point indifferent directions, interference monitoring may be performed inmultiple, if not all, receive channels.

In some embodiments in which more than one receive channel is monitored,the interference monitoring component is replicated for each receivechannel to be monitored. In some such embodiments, the RSSI values fromeach of the interference monitoring component may be combined, e.g.,averaged, and the combined results used to ascertain the presence andproperties of the interference. This approach may be referred to as hardcombining. In another embodiment, the outputs of the moving averagefiltering components of the interference monitoring components arecombined, e.g., averaged, to generate a combined output. Oneinterference threshold component then operates on that combined output.This approach may be referred to as soft combining. These embodimentsmay provide improved interference monitoring performance in terms ofsensitivity to interference and accuracy of identification of the slopeof the interference frequency, etc., at the cost of additional powerconsumption.

In another example, in some embodiments, the IF signals from multiplereceive channels are combined, e.g., by summation, and the combinedsignal provided to a single interference monitoring component. Giventhat the frequency of the interference is expected to vary quickly overany single chirp, such linear combination is acceptable as there is noconcern that the interference signals in different channels willcoherently subtract from each other or coherently reinforce each otherfor all the IF frequencies.

In another example, embodiments have been described herein in whichquantized RSSI numbers are provided to the external processing unit. Oneof ordinary skill in the art will understand embodiments in which theRSSI data is not quantized on the radar SOC.

In another example, embodiments have been described herein in which theRSSI numbers are quantized using three thresholds. One of ordinary skillin the art will understand embodiments in which more or fewer thresholdsare used.

In another example, embodiments have been described herein in which allquantized RSSI numbers are provided to the processing unit, includingthose that indicate little to no interference. One of ordinary skill inthe art will understand embodiments in which those quantized RSSInumbers indicating little to no interference are not provided to theprocessing unit.

In another example, one of ordinary skill in the art will understandembodiments in which one or more of the components of the interferencemonitoring path(s) are programmable.

In another example, embodiments have been described herein in whichinterference monitoring paths do not share components. One of ordinaryskill in the art will understand embodiments in which one or more of thecomponents may be shared between interference monitoring paths.

In another example, embodiments have been described herein in which afrequency shifter component and a low pass filter component are used toextract a sub-band for interference monitoring. One of ordinary skill inthe art will understand embodiments in which a band pass filter is usedinstead. Further, one of ordinary skill in the art will understandembodiments in which rather than having each interference monitoringpath include one or more components to extract a sub-band, a filter bankis used to extract the desired sub-bands for each of the interferencemonitoring paths.

In another example, one of ordinary skill in the art will understandembodiments in which the moving average filter component implements ablock averaging filter in which rather than adding one new sample to thesubset and dropping the oldest sample, a block of new samples may beadded to the subset and a corresponding number of oldest samples isdropped. One of ordinary skill in the art will understand that the useof a block averaging filter reduces the sample rate of the output of themoving average filter component.

In another example, embodiments have been described herein in which theADC in the monitored receive channel is a complex oversampling ADC. Oneof ordinary skill in the art will understand embodiments in which theADC is a complex ADC or an oversampling ADC. In an oversampling realADC, the image band cannot be distinguished from the radar signal band,but multiple bands beyond Nyquist can be observed.

In another example, embodiments have been described herein in whichinterference monitoring is performed in one or both of the imagesub-band and the upper Nyquist sub-band. One of ordinary skill in theart will understand embodiments in which either or both of thesesub-bands is further split into sub-bands for monitoring. Monitoringadditional sub-bands provides better granularity when estimating theslope of an interfering and for handling multiple interfering signals.Further, one of ordinary skill in the art will understand embodiments inwhich sub-bands farther out, e.g., sub-bands of 3rd and/or 4th Nyquistbands, are also monitored for interference.

In another example, determination of RSSI number in multiple sub-bandsmay be implemented by performing a fast Fourier transform (FFT) of theinput to interference monitoring component and summing up the magnitudeor power of the FFT bins corresponding to each sub-band to yield RSSInumbers for each sub-band. The FFT may be performed for many timedurations of samples—one FFT per time duration and the RSSI (or impactindicator) results compared over successive results to identify thedirection and slope of the interference frequency.

In another example, one of ordinary skill in the art will understandembodiments in which the thresholds used by the interference thresholdcomponent may differ for each monitored sub-band. The thresholds fordetecting the presence of the interference and the interference impactmay be designed for each sub-band based on the gain response of thecomponents of the receive channel versus the IF frequency and also thenoise power versus IF frequency. This is particularly applicable for2^(nd) and higher Nyquist bands, where typical receivers may have highernoise power, e.g., those employing Sigma Delta ADCs, and lower gain dueto IF filter droops and the low pass filter nature of IF filters.

In another example, embodiments have been described herein in which theFMCW radar system includes a radar SOC and a processing unit. One ofordinary skill in the art will understand embodiments for other FMCWradar system architectures. Further, one of ordinary skill in the artwill understand embodiments in which the interference monitoringcomponent is on a chip separate from the radar frontend. In suchembodiments, the output of the decimation component 502 may be providedto this chip via a high speed serial interface.

In another example, embodiments have been described herein in which theinterference monitoring is performed in hardware. One of ordinary skillin the art will understand embodiments in which some or all of theinterference monitoring may be implemented in software.

Certain terms are used throughout the description and the claims torefer to particular system components. As one skilled in the art willappreciate, components in radar systems may be referred to by differentnames and/or may be combined in ways not shown herein without departingfrom the described functionality. This document does not intend todistinguish between components that differ in name but not function. Inthe following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” and derivatives thereof are intended to mean an indirect,direct, optical, and/or wireless electrical connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect electrical connection, through an indirect electrical connectionvia other devices and connections, through an optical electricalconnection, and/or through a wireless electrical connection, forexample.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope ofthe disclosure.

What is claimed is:
 1. A frequency modulated continuous wave (FMCW)radar system comprising: a receiver configured to: receive a radarreflection in a chirp; and generate a digital intermediate frequency(IF) signal during the chirp; and an interference monitoring componentcoupled to the receiver and configured to: receive the digital IFsignal; determine at least one sub-band in the digital IF that does notinclude the radar reflection; and monitor the at least one sub-band inthe digital IF signal for interference.
 2. The FMCW radar system ofclaim 1, in which the interference monitoring component is configured tocompute received signal strength indicator (RSSI) values as a functionof time for each sub-band of the at least one sub-band to determinewhether or not interference is present the sub-band.
 3. The FMCW radarsystem of claim 2, in which the interference monitoring component isconfigured to quantize each RSSI value based on at least oneinterference threshold to generate at least one interference impactindicator.
 4. The FMCW radar system of claim 2, in which the at leastone sub-band includes one or both of a sub-band in an image band of thedigital IF signal and a sub-band in an upper Nyquist band of the digitalIF signal.
 5. The FMCW radar system of claim 2, in which RSSI values aregenerated for each chirp of a frame of chirps while a transmitter in theFMCW radar system is on.
 6. The FMCW radar system of claim 1, in whichthe digital IF signal is generated while a transmitter in the FMCW radarsystem is off.
 7. The FMCW radar system of claim 2, in which RSSI valuesare generated for each chirp of a frame of chirps while any transmittersin the FMCW radar system are off between chirps, in which the digital IFsignal is generated during each chirp ramp back and the at least onesub-band is a full bandwidth of the IF signal.
 8. The FMCW radar systemof claim 2, in which the digital IF signal is generated by a scan of afull frequency range of the FMCW radar system prior to transmission of aframe of chirps while any transmitters in the FMCW radar system are off,and in which the at least one sub-band is a full bandwidth of thefrequency range.
 9. The FMCW radar system of claim 2, in which RSSIvalues are generated after one or more chirps of a frame of chirps whileany transmitters in the FMCW radar system are off between the one ormore chirps, in which the digital IF signal is generated by a scan of afull frequency range of the FMCW radar system, and in which the at leastone sub-band is a full bandwidth of the frequency range.
 10. A methodfor interference detection in a frequency modulated continuous wave(FMCW) radar system, the method comprising: receiving, in aninterference monitoring component of the FMCW radar, a digitalintermediate frequency (IF) signal from a receiver in the FMCW radar,wherein the digital IF signal includes a radar reflection; determining,by the interference monitoring component, at least one sub-band in thedigital IF that does not include the radar reflection; and monitoring,by the interference monitoring component, the at least one sub-band inthe digital IF signal for interference.
 11. The method of claim 10, inwhich monitoring includes computing received signal strength indicator(RSSI) values as a function of time for each sub-band of the at leastone sub-band to determine whether or not interference is present thesub-band.
 12. The method of claim 11, in which monitoring includesquantizing each RSSI value based on at least one interference thresholdto generate at least one interference impact indicator.
 13. The methodof claim 11, in which the at least one sub-band includes one or both ofa sub-band of an image band of the digital IF signal and a sub-band ofan upper Nyquist band of the digital IF signal.
 14. The method of claim11, in which RSSI values are generated for each chirp of a frame ofchirps while a transmitter in the FMCW radar system is on.
 15. Themethod of claim 10, in which the digital IF signal is generated while atransmitter in the FMCW radar system is off.
 16. The method of claim 11,in which RSSI values are generated for each chirp of a frame of chirpswhile any transmitters in the FMCW radar system are off between chirps,in which the digital IF signal is generated during each chirp ramp backand the at least one sub-band is a full bandwidth of the IF signal. 17.The method of claim 11, in which the digital IF signal is generated by ascan of a full frequency range of the FMCW radar system prior totransmission of a frame of chirps while any transmitters in the FMCWradar system are off, and in which the at least one sub-band is a fullbandwidth of the frequency range.
 18. The method of claim 11, in whichRSSI values are generated after one or more chirps of a frame of chirpswhile any transmitters in the FMCW radar system are off between the oneor more chirps, in which the digital IF signal is generated by a scan ofa full frequency range of the FMCW radar system, and in which the atleast one sub-band is a full bandwidth of the frequency range.
 19. Afrequency modulated continuous wave (FMCW) radar system comprising: areceiver configured to: generate a digital intermediate frequency (IF)signal during transmission of a frame of chirps; a digital front end(DFE) component coupled to the receiver to receive the digital IFsignal, in which DFE is configured to extract a radar signal band fromthe digital IF signal; and an interference monitoring component coupledto the receiver and configured to: receive the digital IF signal;determine at least one sub-band in the digital IF that does not includethe radar reflection; and monitor the at least one sub-band of aplurality of sub-bands in the digital IF signal for interference. 20.The FMCW radar system of claim 19, in which the interference monitoringcomponent is configured to compute received signal strength indicator(RSSI) values as a function of time for each sub-band of the pluralityof sub-bands to determine whether or not interference is present thesub-band.
 21. The FMCW radar system of claim 20, in which theinterference monitoring component is configured to quantize each RSSIvalue based on at least one interference threshold to generate at leastone interference impact indicator.
 22. The FMCW radar system of claim20, in which the plurality of sub-bands includes one or both of asub-band in an image band of the digital IF signal and a sub-band in anupper Nyquist band of the digital IF signal.